We often have conflict with the developer regarding the bug exists or not.

Sometimes bug itself is the not considered and fixed cause of estimation and budget constraints of the project.

Sometimes communication between the developer and tester are not setup properly cause of that developer may not able to interpret the bug properly.

And sometimes the inputs given by the testers are not enough for the developers to interpret and find the solutions, so they seek for more information from testers.

Sometimes the developers says like the bug should be mapped to few requirements and if it is not mapped then it is not valid bugs. etc.